Perhaps what the OP originally is looking for is that "...if it's a rule it's a rule for all, and if not then it's not...". The only reason the 2m O.B. "rule" is even talked about now is that a) it's still used some places and more importantly b) is WAS a rule at one time. If it never was it would never be talked about. Presently I (as a mythical TD) could evoke a 1.5m O.B. rule if I wished - as long as all participants knew of it beforehand, etc. And this goes for all the other things mentioned by David, Josh, etc. I'm thinking that since local rules can be added to any "situation" (tournament or casual) - some probably needing the PDGA's OK and some not (depending on sanctioning) - the OP is looking for the rules to be written in such a way as to ONLY mention those that are ALWAYS in effect...and let non-rules be evoked per the TD, etc. This may or may not be a tough nut to crack.
It may not have been officially listed as "O.B." but I've heard it dozens of times by dozens of TDs over the years - "If your disc comes to rest 2m above the playing surface you're O.B. Mark directly beneath the disc, then get your disc down and proceed with play from there...with a stroke penalty". THEY (the TDs) always mentioned it as "O.B." (right or wrong - but perception IS reality). So, to them, ANYTHING over 2m above the playing surface WAS an O.B. territory...and if your disc was up there, YOU were O.B. May not have been it 'technically' but it COULD have been (remember, TDs can call anything they want O.B.). And of course it gets back to the discussion of dg NOT having different 'penalty situations' (as does bg) such as O.B., hazard, lateral hazard, lost ball, etc.
I think it would be simpler if they did away with mentioning it altogether IF they (the PDGA) wished to NOT have it (and let the TDs who do want it request a waver...for a 2m, 1.5m, bears are off-limits, and any other arcane / weird "rule" they wish to evoke). In bg, they used to play and have in the rules the concept of "stymie". It no longer is in the rule book because they don't play that any more. Etc.
Just because some TDs say that doesn't make it so. Recall that a shot coming to rest out-of-bounds has three options for the next throw to be taken from, whereas a shot determined to be more than 2m above the playing surface when the 2m-rule is in effect, only has one option. They are not the same.
And no, I do not think a TD can state that is arbitrarily OB is anything over 1.5m off the ground is OB, or 3m off the ground or anything like that. For this type of deviation he'd have to get special permission from the tour manager, which, by definition, doesn't make it as the TD's discretion.